Sizing is a technique which is typically used to control absorption and/or penetration of paper and other cellulosic products by fluids such as water, water-borne compositions, and inks. Paper and other cellulosic products may be sized to a variety of degrees and for a variety of purposes.
Sizing can be carried out before cellulosic product is completely formed by adding an internal sizing agent directly to aqueous pulp slurry to coat the fibers of the pulp or after formation of the finished cellulosic products by applying sizing agents to at least one surface of the product thus filling the capillaries of the product. Surface sizing is generally less expensive than internal sizing, as almost the entire sizing agent is retained on the surface of the treated product.
Many different materials have been employed commercially as surface sizes including synthetic products based on styrene-maleic anhydride (SMA) copolymers and naturally occurring materials such as wax and as internal sizes such as alkenyl succinic anhydride, alkyl ketene dimer or rosin. While there are a variety of known surface sizing systems, a continual need exists for sizing systems that provide improved sizing performance (e.g. lower water absorptiveness as determined by the Cobb method) over known sizing systems.